The research proposed for this award will examine the mechanisms underlying attentional modulation of neuronal activity in primary visual cortex (V1). Visual spatial attention modulates the firing rate of neurons in early visual structures, however how and why attention alters early visual activity remains a mystery. A better understanding of the neural mechanisms underlying attention will lead to improved treatments and therapeutic interventions to increase the quality of life for individuals afflicted with disordrs such as Autism and attention deficit disorder, both characterized by disruptions of attentional processing. In order to examine the mechanisms for spatial attentional modulation of visual activity at the laminar, neuronal, and circuit levels, three experimental aims are proposed. Attentional modulation of visual activity will be assessed across the different cortical layers in 1 (Specific Aim 1), across different physiological neuronal cell types within V1 (Specific Aim 2), and across populations of neurons at different downstream locations relative to thalamocortical inputs to V1 (Specific Aim 3). For each experiment, linear multi-electrode arrays will be used to record single-unit and local field potential activity in V1 of alert primates performing a contrast detection task in which spatial attention is allocated to different locations within the visual fied across trials. Attentional modulation of neuronal activity will be compared to current source density profiles of local field potential activity across layers and visual physiological responses Primate V1 is an ideal model system in which to examine attentional mechanisms because much is known about the neural architecture, morphological and physiological cell types, and local cortical circuits. Additionally, primate V1 is structurally and functionally similar to humanV1 allowing for direct translation of results toward clinical treatments in humans. Through the studies proposed, the applicant will receive new training on multiple experimental techniques including neurophysiological recordings in alert primates. Through the mentorship of the applicant's two co-sponsors, Drs. Briggs and Bucci, the applicant will gain scientific knowledge and expertise in a number of experimental techniques, providing a solid foundation for her future career objectives of studying neural circuit mechanisms of cognitive phenomena as an independent investigator. The combined experience and expertise of the applicant's co-sponsors, along with the excellent training environment available at Dartmouth, will ensure the applicant's successful completion of the proposed research program and will provide her the skills necessary to run her own independent research program in the future.